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In this study, composite ceramic slurries based on submicron-micron-sized cordierite-zirconia were prepared with varied zirconia content. Standard bending strength and fracture toughness testing samples were directly designed and fabricated using stereolithography 3D printing followed by different sintering schemes to study the mechanical reinforcement effect. The physical compositions and microstructures of the samples were characterized. The additively manufactured cordierite-zirconia composites exhibit excellent mechanical properties. Maximum measured bending strength (136 MPa) and fracture toughness (1.8 MPa m1/2) were reached by adding 2 wt% and 6 wt% zirconia, namely an increase of 44% and 66% relative to pure cordierite, respectively. The strengthening and toughening mechanisms of the composites were further explained mainly by microstructural analysis. This study provides an alternative and direct design and manufacturing method for the mechanical measurement and reinforcement of ceramic composite parts based on the use of 3D printing technology.

Strength and ductility were simultaneously enhanced in the additively manufactured CoCrFeMnNi high-entropy alloy by laser powder bed fusion (LBPF) under reactive N2 atmosphere. It was found that ni...

Selective laser melting (SLM) was successfully applied to fabricate strong and ductile reduced activation ferritic/martensitic (RAFM) steel by introducing heterogeneous multi-/bimodal microstructure. The SLM-built RAFM steel exhibited an excellent combination of strength and ductility (i.e. yield strength of 1053 ± 4.7 MPa and elongation of 16.9 ± 0.4%), well surpassing the previously reported counterparts. The superior strength was expected from the refined grains and lath martensites, and the high ductility was associated with the improved dislocation-controlled strain hardening capability. This work provides a basis for developing high-performance RAFM steel by microstructural design via SLM. A new strategy, refers to heterogeneous multi-/bimodal microstructure, is proposed to develop strong and ductile RAFM steel via SLM and the achieved superior mechanical properties overcome the classic strength-ductility trade-off.

This study investigated the effects of hot isostatic pressing (HIP) on the microstructures and mechanical properties of Ti6Al4V fabricated by electron beam melting (EBM). The differences of surface morphologies, internal defects, relative density, microstructures, textures, mechanical properties and tensile fracture between the as-built and HIPed samples were observed using various characterization methods including optical metallography microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD) and tensile tests. It was found that the main effects of HIP on microstructures include&mdash, the increase of average grain size from 7.96 &plusmn, 1.21 &mu, m to 11.34 &plusmn, 1.89 &mu, m, the increase of &alpha, lamellar thickness from 0.71 &plusmn, 0.15 &mu, m to 2.49 &plusmn, 1.29 &mu, m and the increase of &beta, phase ratio from 4.7% to 10.5% in terms of area fraction on the transversal section. The combinatorial effects including densification, increase of grain size, &alpha, lamellar thickness, &beta, phase ratio, reduction of dislocation density and transformation of dislocation patterns contributed to the improvement of elongation and ductility of EBM-fabricated Ti6Al4V. Meanwhile, these effects also resulted in a slight reduction of the yield strength and UTS mainly due to the coarsening effect of HIP.

BACKGROUND. Data are limited on the impact of neuraminidase inhibitor (NAI) treatment on avian influenza A(H7N9) virus RNA shedding. METHODS. In this multicenter, retrospective study, data were collected from adults hospitalized with A(H7N9) infection during 2013–2017 in China. We compared clinical features and A(H7N9) shedding among patients with different NAI doses and combination therapies and evaluated factors associated with A(H7N9) shedding, using Cox proportional hazards regression. RESULTS. Among 478 patients, the median age was 56 years, 71% were male, and 37% died. The median time from illness onset to NAI treatment initiation was 8 days (interquartile range [IQR], 6–10 days), and the median duration of A(H7N9) RNA detection from onset was 15.5 days (IQR, 12–20 days). A(H7N9) RNA shedding was shorter in survivors than in patients who died (P < .001). Corticosteroid administration (hazard ratio [HR], 0.62 [95% confidence interval {CI}, .50-.77]) and delayed NAI treatment (HR, 0.90 [95% CI, .91-.96]) were independent risk factors for prolonged A(H7N9) shedding. There was no significant difference in A(H7N9) shedding duration between NAI combination treatment and monotherapy (P = .65) or between standard-dose and double-dose oseltamivir treatment (P = .70). CONCLUSIONS. Corticosteroid therapy and delayed NAI treatment were associated with prolonged A(H7N9) RNA shedding. NAI combination therapy and double-dose oseltamivir treatment were not associated with a reduced A(H7N9) shedding duration as compared to standard-dose oseltamivir.

Selective laser melting (SLM) was applied to fabricate high-strength and ductile reduced activation ferritic/martensitic (RAFM) steel via modification of heterogeneous microstructure that consists of domains of fine and coarse grains as well as lath martensites, but with different grain morphology in respond to the variation in the scanning strategy and resultant thermal history. The SLM-built RAFM steel exhibited an enhanced strength-ductility synergy with high yield strength of 967 MPa and high elongation of 15.1% under a meander scanning strategy, surpassing the previously reported counterparts, which was ascribed to the refined microstructure and improved strain hardening. In contrast, an island scanning strategy deteriorated the ductility down to 3.8% arising from the oriented alignment of columnar coarse grains around island, which initiated micro-voids and cracks during deformation and finally gave rise to a premature failure. This work proposed the microstructural design principles for additively manufacturing high-performance RAFM steels and is expected to facilitate their application in the fusion reactor.

Relatively low dimensional accuracy and poor surface quality have been the major drawbacks for selective laser melting (SLM). A hybrid SLM and computer numerical control (CNC) milling system that operates in an alternating manner may have the capability of improving the dimensional accuracy and surface quality to a comparable level to conventional CNC processes. However, very few studies have been conducted on the machine development and experimental applications of this hybrid process. In this study, we developed a hybrid SLM/CNC milling system based on the fundamental understanding of the hybrid process. Key technological challenges are analyzed including the mechanical design of the hybrid machine to solve the design contradictions in hybridizing the two processes, the adaption of laser scanning system to avoid structural interferences between SLM and CNC, and the process planning and data processing to coordinate SLM and CNC milling. Solutions are proposed to address these challenges. The hybrid system developed in this study was then validated with commonly used stainless steel 316 L. Nearly full dense 316 L parts with relative density ≥99 % were fabricated. Excellent tensile properties with yield strength ≥540 MPa, ultimate strength ≥650 MPa and elongation ≥44.5 % that are comparable to the conventional solely SLMed ones were obtained. Meanwhile, the dimensional accuracy and surface roughness were also significantly improved with this hybrid system. This systematic study further suggests that the hybrid SLM/CNC milling system can be an effective and promising tool for the manufacturing of high-quality metal parts.

Two types of scanning strategies were adopted to study the effect of scanning strategy, i.e., bidirectional scanning without (SS-X) and with 45° deviation from X/Y-axis and 90° rotation (SS-XY45) between adjacent layers, on microstructure and mechanical properties of reduced activation ferritic/martensitic (RAFM) steel fabricated by selective laser melting (SLM). The SLM-built RAFM steel exhibited a better combination of strength and ductility than the previously reported counterparts. The SS-X had higher yield strength of 911 MPa and higher elongation of 18.7% than the SS-XY with yield strength of 893 MPa and elongation of 15.0%. The results reveal that the variation in the yield strength was mainly ascribed to the different grain size and the improved ductility was associated with the modified grain structure that altered the tensile fracture mode with concurrent occurrence of intergranular brittle and transgranular ductile fracture. This finding provides an alternative to fabricate high-performance RAFM steel by tailoring the microstructure with different scanning strategies.